Forming means for profile grinding wheels



5 Sheets-Sheet 1 Filed Dec. 9, 1944 "m Any CQ B. A. PORTER ET AL FORMING MEANS FOR PROFILE GRINDING WHEELS May 10, 1949.

5 Sheets-Sheet 2 Filed Dec. 9, 1944 Fig. 2.

i e -z sn 7/104 arr May 10, 1949. c. B. A. PORTER ETAL 2,469,844

FORMING MEANS FOR PROFILE GRINDING WHEELS 5 Sheets-Sheet 3 Filed Dec. 9, 1944 May 10, 1949.

C. B. A. PORTER ET AL FORMING MEANS FOR PROFILE GRINDING WHEELS 5 SheetsSheet 4 Filed Dec. 9, 1944 JCL .z. H1

y 1949- c. B. A. PORTER EI'AL 2,469,844

FORMING mmus FOR PROFILE GRINDING WHEELS Filed Dec. 9, 1944 Y 5 Shets-Sheet 5 Patented May 10, 1949 FORMING MEANS FOR PROFILE GRINDING WHEELS Charles Benjamin Albert Porter and Clifford Percy Seymour, Hillingdon, England, assignors to Harold Stuart Hallewell, Hayes, Middlesex,

England Application December 9, 1944, SerialNo. 367,398 In Great Britain December 21, 1943 12 Claims.

This invention relates to the formation on a grinding wheel of a, profile, which is the complement of a profile required to be ground thereby on a tool, die, gauge or other work-piece, by

means of a dressing tool point operated by a or nearly radial with respect to the axis of rotation of the grinding wheel and which faces right or left as required. I

Another object is to prevent inadvertent cutting of the dressing tool by a projecting part of the profile of the grinding wheel.

Another object is to facilitate the control of such apparatus so as to permit the dressing tool to traverse the whole face of the grinding wheel in an uninterrupted sweep, which avoids the blemishes that would otherwise result from discontinuous application of the dressing tool to the wheel.

Another object is to improve the accuracy and durability of the mechanism.

Another object is to provide the improved mechanism in one form suitable for use with a conventional surface grinder and in another form suitable for use with a conventional centre grinder.

Embodiments of the invention will be de scribed by way of example with reference to the accompanying drawings,in which:

Fig. 1 is a perspective diagrammatic drawing of an elementary form of apparatus according to the invention, for use with a surface grinder,

Fig. 2 is a side elevation of a preferred arrangement of apparatus developed from the form shown in Fig. 1,

Fig. 3 is an end elevation, as seen from the right-hand side of Fig. 2,

.Fig. 4 is a plan of the same apparatus.

Fig. 5 is a section to a larger scale, taken on the line 5-5 in Fig. 4,

Fig. 6 is a sectional side elevation of part of the apparatus, taken on the line 6-6 in Fig. 3,

Fig. '7 is a section to a larger scale, taken on the line 1-l in Fig. 4,

Fig. 8 is a plan of a part of the elements shown in Fig. '7, 1

Figs. 9 and 10 are respectively a rear anda side elevation of a detail, also shown to a larger scale,

Fig. 11 is a perspective diagrammatic drawing of an elementary form of apparatus for use with a centre grinder, and

Figs. 12 to 18 are diagrams illustrating uses of the improved apparatus.

The embodiment shown in Fig. 1 includes a rectangular base plate 20 adapted to be engaged by the magnetic chuck 2i of a surface grinder and has a depending flange 22 at one edge which serves to locate the base'square with respect to the grinder. A tubular bracket 23 rigid with the base adjustably carries a board 24 to which is fixed a positive template 25 lying in a vertical plane parallel to the axis of the grinding wheel; the template has two straightedges 25A and 25B adjoining each other at right angles, and the board 24 includes a horizontal straight-edge 2'6 and an end stop 21 co-operating with the straight edgesof the template 30 so as to locate the template in a predetermined position. The pantograph linkage includes a more or less horizontal long link 28 pivoted on a bearing pin 29 mounted on the base 20 with its axis horizontal and perpendicular to the plane of the template. A short more or less vertical link 30 is also pivoted on the pin 29. A lever 3| parallel to the short link 30 is pivoted to the free end of .the long link 28 and carries the template follower 33 at its upper end. A second lever 32 parallel to the longlink 28 is connected between the upper end of the] short link 30 and a point on the template-follower lever 3 I The lever 32 carries the wheel-dressing tool 34 at a point near its end that is pivoted to the, shortlink 30.

The template follower 33 is formed by a horizontal pin journalled in the upper end of the lever 3|. To the end of the pin 33 is fitted a sector-section blade 35.

The dressing tool is a diamond-pointed needleshapedtool 34 of conventional type carried in one arm of an angle bracket 36 the other arm of which is rigid with. a horizontal pin 31 journalled in the lever 32, the arrangement being such that the diamond tool 34 can be set below the wheel 38 with the centre about which its radiused point is formed on the axis 39 of the bearing pin 31 and with the axis of the tool displaceab-le in the vertical plane containing the axis of the grinding wheel. The radius of the template. follower pin 33 is equal to the radius of the diamond point of thedressing tool 34 multiplied by the mechanical advantage of the pantograph linkage, which may be 6 or 10 to 1.

The template-follower pin 33 and the diamondholder pin 31 are connected for rocking in unison under control of a hand-wheel 40 on the former pin. The necessary connection consists of cranks 4| and 42 fast on the respective pins, and connecting links 43 and 44 couplingthese cranks to the two arms respectively of a bell crank lever 45 pivotedabout the axis of the connection between the two pantognaphlevers 3| and 32.

For convenience of explanation, it will be assumed that the grinding wheel is required to have a surface which includes a cylindrical portion, denoted by 46 on the template 2i, bearing a circumferential flange having plane sides as indicated at 41. The sector 35 attached to the follower pin has an apex angle slightly exceeding the apex angle of the dressing tool. The template 25 is set in such a way as to be similar in attitude to the intended profile oi the bottom of the wheel 38. After the grinding wheel has been dressed, if desired by means of a roughing diamond, to approximately the desired profile, the final traverse of the wheel i made, by a finishing diamond substituted it necessary for the roughing diamond, by the operator's manipulating the pantograph by means of the hand-wheel 40 in such a way as to cause the template follower 33 to traverse the edge of the template in a continuous movement. Since the template follower and the diamond can be displaced in unison about the horizontal rocking axes of their pins by means of the hand-wheel 40 while the latter is being used to operate the pantograph, the template-follower and the diamond can be adjusted from time to time about these axes as is necessary to enable them to trace both fianks of the flange portion 41 without interrupting the continuous traverse of the diamond across the wheel. Furthermore, the sector 35 prevents the template follower from being accidentally manipulated in such a way that the shoulder of the dressing tool is cut by a part of the wheel.

In the preferred construction shown in Figs. 2 to 10, parts corresponding to those already described and shown in Fig. 1 are denoted by the same reference numerals with the addition of the letter A. The modifications adopted in this practical machine are concerned primarily with securing rigidity, accuracy and ease of operation, together with the ability to maintain accuracy after considerable use.

Features contributing to these aims are the selection of conical spigot-and-socket bearings for the pivotal connections of the pantograph linkage, and of preloaded anti-friction bearings (i. e. of the ball or conical-roller type) for mounting the dressing-tool holder in the pantograph mechanism.

The apparatus may also include a board on which can be mounted a template having two straight edges adjoining each other at right angles, said board including means 26A andf2lA, corresponding to the means 28 and 21 hereinbefore described with reference to Fig. 1, for cooperating with said edges so as to locate the template in a predetermined position.

The pantograph mechanism may include a link parallelogram two opposite sides of which are constituted by two channel-section bars nested to form a box-section assembly, and the side walls of these bars conveniently comprise housings for the pivot pins of the conical bearings.

The lever 32A is a light alloy casting of inverted channel section having boxed-in ends, while the link 28A is a channel-section light alloy casting nested within the channel 32A, so that dust is largely excluded from the bearings contained in the interior of this box-like assembly.

The link 28A is pivoted on the base by hardened and ground steel conical bearings, and the link 30A is pivoted-on the link 28A by similar bearings, both sets of bearings having common axial loading means. As shown particularly in Fig. 3 and Fig. 5, the base 20 has two bearing lugs 50 and II, the latter forming part of a cylindrical socket 52 in which the tubular bracket 23A is clamped by screws 53. A cone-headed pin 54 is a driving fit in the lug 50, and a cone-headed pin 55 is a close sliding fit in the lug 5|; it can be adjusted axially by a screw 56 (Figs. 3 and 4) engaged in the outer end of the lug, and it is locked by a grub screw 51. The pins 54 and 55 cooperate respectively with two pins 58 and 59 which are a sliding fit in the sides of the link 28A and which have conically counterbored heads at their outer ends. The inner ends of the pins 58 and El are conical and engage in conical counterbores in the ends of a pin I. which is a driving fit in the link "A. The screw 58 serves to apply axial loading to both pairs of bearings simultaneously. When the desired axial loading has been applied by the screw 56, the pins 58 and 59 are locked in the link 28A by clamping screws 8|.

The pivotal connection between the link 30A and the lever 32A is eiiected by hollow hardened and ground conical ended pins 62 and 63; these pins are a close sliding lit in the walls of the lever 32A and they engage in conical counterbores in the ends of a hollow pin 64 which is a driving fit in the link A. The bearings are axially loaded by a screw 65 passing through the pinsand tensioned by a nut 66 provided with a locking screw 61.

The lever 3IA consists of a tubular shank the lower end of which is fixed in a lug 68 (Fig. 6) integral with a body 89 pivotally connected to the link 28A and the lever 32A by bearings which are similar to'those shown in the upper part of Fig. 5. As shown in Fig. 6, the bell-crank lever 45A has a bearing on a projecting end of the bush 64' which corresponds to the bush 64 in Fig. 5.

The bearing pin 31A of the dressing tool holder is mounted in the lever 32A by preloaded ball bearings, as shown in Fig. 7. The outer races 10 of the two bearings are fitted in bores in the lever 32A and abut against locating surfaces ll. One inner race 12 is located by a shoulder 13 on the pin 31A while the other inner race 12' is spaced from the race 12 by shims 14, a boss 15 of the lever 42A and a distance piece 76. A nut 11, provided with a locking screw 18 and engaged on a, threaded end portion of the pin 31A acts through a distance piece 19 to clamp the two inner races and the said intervening elements together. The bearings are designed to carry substantial axial loading applied in such a direction to the inner races as to urge the outer races against the abutment shoulders H. The shims are such as to give the necessary axial loading of the ball bearings when the nut TI is screwed tight, and when this adjustment has been made, the lever 42A is secured by tightening a pinch bolt 80. Felt rings 49 protect the bearings from abrasive dust. The angle bracket 36A is integral with the pin 31A and terminates in a block 8| to which are screwed parallel side plates 82. A block 83 having a V notch 84 is slidably fitted between the side plates 82 and has a transversely slotted outer end guided on a rectangular bar 85 carried by trunnions 8B in the side plates 82. A screw 81 fitted in a tapped hole in the bar 85 engages the block 83. The V notch, is symmetrical with respect to a plane containing the axis 39A of the pin 31A, so that when the cylindrical shank of the dressing tool 34A is gripped between the V notch and the outer end face of the block 8|, as a result of tightening the screw 81, the axis of the tool cuts the axis 39A. A plate 88 is screwed to the under side of the block BI and supports the end of the dressing tool by means of an adjusting screw 88' having a graduated head. The upper face of the block 8| is plane and parallel to and at a known distance d from the axis 39A. The dressing tool can therefore be readily set to the correct height by means of a gauge located by the said face of the block 8|. Alternatively, or in addition, the upper face of the lever 32A may be machined plane and parallel to the axis 39A; a dial gauge located by this face and engaging the tip of the dressing tool will indicate correct setting of this tool by giving a constant reading as the bearing pin 31A is rocked.

The template follower includes a hollow shaft 33' having a taper socket at one end to fit a tapered shank of the follower pin 33A and having the handwheel 40A fast on the other end. The shaft 33 is carried, by means of a preloaded ballbearing assembly generally similar to that shown in Fig. '7, in a head 89 fixed to theupper end of the tubular shank of the lever 3IA. The sector 35A is carried by a bracket 90 a hub of which is adjustably fixed to the shaft 33' by a grub screw 9|. The follower pin 33A is retainedby a screw 99 fitted through the hollow shaft 33' and can be changed to match different forms of dressing tool.

The shank of the lever 3IA operates" between two guide rails 92 fixed to the board 24A by brackets 93 and serving to prevent accidental straining of the pantograph mechanism.

In order to relieve the operator of most of the weight of the pantograph mechanism, a bellcrank lever 94 (Fig. 6), pivoted to a lug 95 on the link 28A, has one arm coupled to a tension spring,

96 anchored at 91 to the link 28A. The other arm of this lever passes through a slot in the link 28A and rides on a hardened block 98 fixed to the base 20A. The spring 96 is preferably so set that the template follower will still fall away from the template; if the spring were to overbalance the weight of the pantograph mechanism, there would be more risk of thedressing tools accidentally plunging too deeply into the wheel.

While the forms of the improved apparatus so far described include a base adapted to be engaged by the magnetic chuck of a surface grinder and provided with a locating fiange, another convenient form includes a frame having a portion adapted to be mounted between the centres of a centre grinder.

Fig. 11 shows apparatus for use on 'centre grinders. Parts corresponding to those already described and shown in Fig. 1 are denoted by the same reference numerals with the addition of the letter B. The frame includes a centring portion 203 adapted to be mounted between the centres of the grinder, a part of which is shown in Fig. 11 and denoted by I00, and a template bracket 23B rigid with the portion 20B and provided with a board 24B adapted to carry a template 25B on the side of the centre axis remote from the grinding wheel B, the fixed pivot pin 29B of the pantograph linkage being carried by the centring portion 203 with its-axis perpendicular to the plane of the template.

The pantograph linkage consists of a lever IOI lying more or less longitudinally and pivoted part way along its length to the pin 293. A short link 30B is pivoted about an axis perpendicular to the plane of the template to the end of the shorter arm of the lever IOI and extends towards the grinding wheel. A template-follower lever 3IB is pivoted part way along its length to the end of the longer arm of the lever WI and lies parallel to the short-link 3013. The shorter arm of the template-follower lever 3IB is pivoted to a long link I02 parallel to the lever IOI and on the side thereof nearer the wheel. The links 30B and I02 are pivotally connected together about an axis which is also the axis of rocking adjustment of the diamond tool holder 36B carried by these links, The diamond tool 343 is so placed that its point moves in a plane containing the axis of the grinding wheel and parallel to the template. The template follower 33B is worked on the edge of the template nearer the centre axis by an operator holding the hand-wheel 40B, and the template is a positive and inverted mamtude with respect to the desired profile of the nearest part of the grinding wheel. This apparatus has its diamond tool holder and template follower interconnected for angular adjustment in unison with and in response to rocking of the hand whee-l 40B similarly to those described with reference to Fig. 1, and can be operated in a corresponding manner- As an alternative to the needle shaped diamond tool, it may be necessary, in the improved apparatus, to use a chisel-pointed diamond for added strength on very small radii. The end face of the block 8I shown in Figs. '7 and 8 in this case cooperates with a flat on the shank of the diamond tool to locate the chisel edge in the plane ofrotation of the grinding wheel.

It is sometimes required to form on the grinding wheel a profile having a re-entrant corner which is sharper than the radiused point of the dressing tool. It is also sometimes found that, in order to form one part of the profile on the grinding wheel, the dressing tool would have to assume such an attitude that its shank would foul another part of the profile. An example of a formed work-piece presenting these difficulties is shown in Fig. 12; this is a female die for use in the pressing of half anodes for radio valves, the channels I03 and I04 taking part respectively in the formation of grooves accommodating the anode supports and the'operative portion of the electrode. If it were attempted to form on a grinding wheel a profile which was the complement of Fig, 12, the re-entrant corners adjoining the portions I03 and I04 would have a radius equal at least to the radius'of the point of the dressing tool, whereas they are required to be substantially sharper. Furthermore, the projecting portion corresponding to I04 would prevent access of the tool to the inner corners adjoining the portions corresponding to I03.

Thus a method of producing the required profile on the work-piece involves the use of two separate grinding operations in which respectively there are used two different wheel profiles which, when superimposed, produce the complement of the said required profile. In order toform a sharp reentrant corner in the profile of the work-piece, the two portions of the profile that adjoin each other at the corner are ground respectively by the said two distinct grinding operations,

In the particular problem illustrated by Fig. 12, the work-piece is profile ground in two stages by two wheels. Fig. 13 shows the profile of one of the wheels; this has a ridge I04 bordered by depressions I05 which are deep enough to allow the dressing tool 34 to continue the flanks of the ridge I04 to below the level of the cylindrical part I00 of the'profile. This wheel is used to form the channel I04 in the work-piece (Fig. 14)

aeeaeaa it leaves thetwo shallow ribs I115. The profile olthe other wheel (Fig. 15) has .two ridges I03 each bordered by depressions I06 serving to allow the dressing tool to continue the flanks of these ridges to belowflthe level of the cylindrical part of the profile. This wheel is used to out only the channels I" in the work-piece and to remove the ridges I05.

Figs. 16 and 17 show the profiles of two other forms of wheels used in succession on one workpiece in order to form the profile shown in Fig. 18.

When the width of the work-piece required to be ground exceeds the capacity of the pantograph mechanism, a part of the profile of the work-piece is formed by one wheel; thereafter the template is changed and the same wheel or another wheel is dressed to the required profile, the work is indexed relatively to the wheel through a distance corresponding to the width of the first wheel, and the remainder of the profile is formed.

The straight edge 26 and the stop 21 provided for location of the template enable one template to be replaced by another with its working-edge in an accurately predetermined position, as is necessary in using the same apparatus for performing successive profile grinding operations on a work-piece.

In order to enable an operator to make sure that the finishing cut of the dressing tool is being properly made, an electrical signalling system may be provided, as shown in Fig. 1. A lamp I! is connected in series with a source I08 of current between thetemplate 25 and the frame of the machine. The board 24 insulates the template from the frame of the machine, and the sector 35 is also made of electrically insulating material. While the follower pin 33 1s in contact with the template, it completes the circuit and the lamp glows. If the follower pin leaves the working edge of the template, the lamp is extinguished.

The dressing-tool holder may carry two dressing tools spaced apart along the axis 39A and used for roughing and finishing respectively.

We claim:

1. Grinding wheel profiling apparatus including a frame capable of being mounted on a grinding machine, a holder for a plane template rigid with said frame, a pantograph linkage pivotally mounted on said frame, a template-follower member mounted on said linkage for rocking about an axis perpendicular to said template, a dressing-tool holder mounted on said linkage for rocking about an axis perpendicular to the plane of said template, a dressing tool mounted in said holder and having a radiused tip so set thatthe ing a link parallelogram which is pivotally mounted on said frame and two opposite sides of which are constituted by two channel-section bars nested to form a box-section assembly, a tem- ,plate-follower member mounted on said linkage centre about which said radiused tip i formed is on the said rocking axis of the dressing-tool holder, the said template-follower member having a working tip which is geometrically similar in section to the section of the said tip of the dressing tool, and the ratio of the radii of the said two tips being equal to the mechanical advantage of the pantograph mechanism, coupling means between said template-follower member and said dressing-tool holder for constraining them to rock in unison, and an element rigid with said template-follower member and co-operating with the template to prevent displacements of the dressing tool such as to cause the shoulder of the dressing tool to be cut by the grinding wheel.

2. Grinding wheel profiling apparatus including a frame capable of being mounted on a grinding machine, a holder for a plane template rigid with said frame, a pantograph linkage compris-.

and a dressing-tool holder mounted on one of said channel-section bars for rocking about an axis perpendicular to the plane of said template, said dressing-tool holder being capable of holding a dressing tool with its tip on the last-mentioned axis.

3. Grinding wheel profiling apparatus including a frame capable of being mounted on a grinding machine, a holder for a plane template rigid with said frame, a pantograph linkage comprising a link parallelogram the two longer sides of which are constituted by two channel-section bars nested to form a box-section assembly and each of. the two shorter sides of which is an element pivotally connected to each of said channel sec tion bars by a bearing comprising a first pin fast in said element, a pair of pins co-operating respectively with the ends of said first pin by means of conical spigot and socket connections, the pins of said pair being mounted in the respective side walls of the appropriate one of said channel-section bars in such a manner as to be relatively displaceable in the axial direction, and adjusting means for urging one ofthe pins of said pair towards the other.

4. Grinding wheel profiling apparatus suitable for use with a, conventional surface grinder, said apparatus including a frame having a plane under surface for engagementby the magnetic chuck of the grinder and provided with a flange for locating against an edge of the magnetic chuck, a holder for a plane template rigid with said frame, a pantograph linkage pivotally mounted on said frame, a template-follower member mounted on said linkage for rocking about an axis perpendicular to said template, a dressing-tool holder mounted on said linkage for rocking about an axis which, when the apparatus is in use, is tangential to the grinding wheel, said dressingtool holder being capable of holding a dressing tool with its tip on the last-mentioned axis, and coupling means between said template-follower member and said dressing-tool holder for constrainin them to rock in unison.

5. Grinding wheel profiling apparatus suitable for use with a conventional center grinder, said apparatus including a frame having a portion capable of being mounted between the centres of the grinder, a holder for a plane template rigid with said frame, a pantograph linkage pivotally mounted on said frame, a template-follower dressing tool with its tip on the last-mentioned axis.

6. Grinding wheel profiling apparatus including a frame capable of being mounted on a grinding machine, a metal template rigid with said frame, a pantograph linkage pivotallymounted on said frame, a metal template-follower member mounted on said linkage, a wheel-dressing tool mounted on said linkage, means electrically insulating said template from said template-follower member, and an electrical circuit which includes a source of current in series with a current-responsive signal device connected between said template and saidrtemplate-follower mem- 9 ber and which is closed, during normal operation, only by contact of said template-follower member with said template.

7. Grinding wheel profiling apparatus includa frame, a holder for a template rigid with said frame, a pantograph mechanism pivotally mounted on said frame and carrying a dressingtool holder capable of being rocked about an axis which is perpendicular to the plane of the template and a template-follower member adapted to be rocked about an axis which is perpendicular to the plane of the template, an operative connection supplementary to the pantograph mechanism for constraining said dressing-tool holder and said template-follower member to rock in unison, and means rigid with said templatefollower member for cooperation with the template to prevent displacements of the dressing tool such as to cause a shoulder of the dressing tool to be cut by the grinding wheel.

8. Apparatus as claimed in claim 7, wherein said dressing tool has a conical nose, and said 10 11. Grinding wheel profiling apparatus including a frame having a base plate provided with a plane under surface capable of being detachably mounted on the work table of a surface grinder, and with a flange along one side of said surface for locating against one edge of the work table,

, a holder for a plane template rigid with said means are constituted by a sector-shaped memher the angle of which is not less than the apex angle of said conical nose.

9. Grinding wheel profiling apparatus including a frame capable of being mounted on a grinding machine, a holder for a plane template rigid with said frame, a pantograph linkage which is pivotally mounted on said frame, a template-follower member mounted on said linkage for rocking about an axis perpendicular to said template, and a dressing-tool holder mounted on said linkage for rocking about an axis which is perpendicular to the plane of the template, said dressingtool holder being capable of holding a dressing tool with its tip on the last-mentioned axis, and a pivotal connection between two elements of the pantograph linkage including a hollow pin fast in one of said elements, apair of pins cooperating respectively with the ends of said hollow pin by means of conical spigot-and-socket connections, the pins of said pair being so mounted in the other of said elements as to be relatively displaceable in the axial direction, and a tension bolt passing through said hollow pin and urging the said pins of said pair towards each other.

10. Grinding wheel profiling apparatus including a frame capable of being mounted on a grinding machine, a holder for a plane template rigid with said frame, a pantograph linkage which is pivotally mounted on said frame, a template-follower member mounted on said linkage for rocking about an axis perpendicular to said template, and a dressing-tool holder mounted on said linkage for rocking about an axis which is perpendicular to the plane of the template, said dressingtool holder being capable of holding a dressing tool with its tip on the last-mentioned axis, and a pivotal connection between said frame and two elements of the pantograph linkage including a first pin fast in one of said elements, a first pair of pins cooperating respectively with the ends of said first pin by means of conical spigot-and socket connections, the pins of said pair being so mounted in the other of said elements as to be relatively displaceable in the axial direction, a second pair of pins cooperating respectively with the respective outer ends of the first of said pairs of pins by means of conical spigot-and-socket connections, the pins of said second pair being so mounted in said frame as to be relatively displaceable in the axial direction, and adjusting means on said frame for urging the pins of said second pair towards each other.

frame, a pantograph mechanism pivotally mounted on said frame, a dressing-tool holder rotatably mounted on the pantograph mechanism for rocking about an axis which is perpendicular to the plane of the template, a templatefollower member rotatably mounted on the pantograph mechanism for rocking about an axis which is perpendicular to the plane of the template, a control handle rotatably mounted on the pantograph mechanism in the neighborhood of said template-follower member, an operative connection supplementary to the pantograph mechanism and connecting said control handle to said dressing-tool holder and said template-follower member, said control handle, when displaced bodily, causing said template-follower member to move bodily along the template, and, when rocked,

- causing said template-follower member and said dressing-tool holder to rock in unison with and in response to rocking of said control handle.

12. Apparatus as claimed in claim 11, and including a dressing tool mounted in said dressingtool holder, wherein said dressing tool has a radiused tip so set that the center about which said radiused tip is formed is on the said rocking axis of the dressing-tool holder, the said template-follower member having a working tip which is geometrically similar in section to the section of the said tip of the dressing tool, and the ratio of the radii of the said two tips being equal to the mechanical advantage of the pantograph mechanism, and wherein said templatefollower member includes an element .co-operating with the template to prevent displacements of the dressing tool such as to cause the shoulder of the dressing tool to be cut by the grinding wheel.

CHARLES BENJAMIN ALBERT PORTER. CLIFFORD PERCY SEYMOUR.

REFERENCES CITED The following references are of record in the file of this patent:

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